With the development of a reproducible assay for suppressor cell activity, this assay is now ready for application to clinical situations. The assay methods will be compared initially with easier mixing experiments in which suspected suppressor cells are admixed with an indicator system and their effect in inducing suppression is compared to normal cells. There are no control cells added in these studies and we believe the spontaneous suppressor cell assay that we have developed will be superior. Initially, studies will be performed on cord blood cells reported to exhibit high spontaneous suppressor cell activity. In addition to these studies, many experiments will be established to determine the nature of the cell responsible for spontaneous suppressor cell activity and the kinetics of the regulation so induced.